This invention relates generally to traction vehicles such as locomotives that have thermal prime movers on board and more particularly to operating locomotives inside of tunnels.
Large self-propelled traction vehicles such as locomotives commonly use a thermal prime mover to drive a generator. The generator supplies electric current to a plurality of direct current (dc) traction motors whose rotors are drivingly coupled to respective axle-wheel sets of the vehicle. The generator typically comprises a main 3-phase traction alternator whose rotor is mechanically coupled to the output shaft of the prime mover (typically a 16-cylinder turbocharged diesel engine). When excitation current is supplied to field windings on the rotating rotor, alternating voltages are generated in the 3-phase stator windings of the alternator. These voltages are rectified and applied to the armature windings of the traction motors. Alternatively, alternating current (ac) traction motors could be used, in which case suitably controlled electric power inverters would be connected between the respective motors and the alternator.
During its normal propulsion mode of operation, a locomotive diesel engine tends to deliver constant power, depending on throttle setting and ambient conditions, regardless of locomotive speed. For maximum performance, the electrical power output of the alternator must be suitably controlled so that the locomotive utilizes full engine power. However, the load on the engine must not exceed whatever level of power the engine can develop. Overloads can cause premature wear, engine stalling, or other undesirable effects. Historically, locomotive control systems have been designed so that the operator can select the desired level of traction power in discrete steps between zero and maximum, and so that the engine develops whatever level of power the traction and any auxiliary loads demand.
Locomotive control systems also typically include suitable means for overriding normal propulsion operation in response to certain abnormal conditions. The response to such abnormal conditions is to reduce or "derate" engine load. This helps the locomotive recover from the abnormal condition and/or prevents serious damage to the engine. One condition which requires derating locomotive power output is excessive engine heat. Typically, the temperature of the engine cooling system is monitored to determine whether the engine load needs to be derated because of overheating. Under this system, unusually high ambient air temperature can cause deration even though there is no malfunction of the engine or its cooling system. This is particularly a problem for multiple-locomotive trains operating within long, narrow tunnels where the trailing units are exposed to high ambient temperatures produced by the exhaust of the leading units. The high ambient temperatures, which can approach 150.degree. C., cause the trailing units to overheat. The resulting deration of the overheated locomotives in a tunnel will adversely affect performance, thereby undesirably increasing running time and decreasing productivity.
Locomotive deration in response to temporary overheating caused by tunnel operation is not really necessary as long as the engine and its various support systems are functioning properly and as long as the locomotive is not inside the tunnel too long. Locomotive components ordinarily have short-time ratings that appreciably exceed their ratings for continuous duty, and therefore a locomotive can safely endure overheating caused by a tunnel environment for short periods (e.g., under approximately ten minutes). Accordingly, when a locomotive engine is temporarily overheated because the locomotive is passing through a tunnel, it is both desirable and feasible to cancel or delay the normal temperature-responsive deration that is provided in prior art locomotive propulsion systems.
U.S. Pat. No. 4,698,761, issued Oct. 6, 1987 to Charles E. Cooper et al., describes a system for a diesel-electric locomotive which automatically detects when the locomotive is in a tunnel. The system monitors the temperatures of the cooling system and the engine lubricant and indicates that the locomotive is in a tunnel if the coolant temperature exceeds an abnormally high magnitude and is higher than a variable reference level that depends on the lubricant temperature. When a tunnel is thus detected, the normal deration function is temporarily suppressed to delay deration. The system shifts the over temperature threshold to a second level which is higher than the level at which deration is normally initiated. Consequently, the engine is allowed to reach a higher temperature before locomotive power is derated while the locomotive is temporarily inside a tunnel. While this system is effective, it only reacts to the high tunnel temperatures after the locomotive or locomotives are already in a tunnel.
Accordingly, there is a need for a locomotive control scheme which can anticipate an approaching tunnel to maximize the time in the tunnel without overheating, thereby avoiding unnecessary tunnel derating.